A high demand presently exists for disc drive memory systems, which are widely utilized throughout the world today in traditional computing environments and more recently in additional environments. These disc drive memory systems are used by computers and more recently by devices including digital cameras, digital video recorders, laser printers, photo copiers, jukeboxes, video games and personal music players. Consequently, the demands on disc drive memory systems has intensified because of increased performance demands and new environments for usage.
Disc drive memory systems store digital information that is recorded on concentric tracks of a magnetic disc medium. Several discs are rotatably mounted on a spindle, and the information, which can be stored in the form of magnetic transitions within the discs, is accessed using read/write heads or transducers. The read/write heads are located on a pivoting arm that moves radially over the surface of the disc. The discs are rotated at high speeds during operation using an electric motor located inside a hub or below the discs. Magnets on the hub interact with a stator to cause rotation of the hub relative to the shaft. One type of motor is known as an in-hub or in-spindle motor, which typically has a spindle mounted by means of a bearing system to a motor shaft disposed in the center of the hub. The bearings permit rotational movement between the shaft and the hub, while maintaining alignment of the spindle to the shaft. The read/write heads must be accurately aligned with the storage tracks on the disc to ensure the proper reading and writing of information.
Spindle motors have in the past used conventional ball bearings between the hub and the shaft. However, the demand for increased storage capacity and smaller disc drives has led to the read/write head being placed increasingly close to the disc surface. The close proximity requires that the disc rotate substantially in a single plane. A slight wobble or run-out in disc rotation can cause the disc to strike the read/write head, possibly damaging the disc drive and resulting in loss of data. Conventional ball bearings exhibit shortcomings in regard to these concerns. Imperfections in the raceways and ball bearing spheres result in vibrations. Also, resistance to mechanical shock and vibration is poor in the case of ball bearings, because of low damping. Vibrations and mechanical shock can result in misalignment between data tracks and the read/write transducer. These shortcomings limit the data track density and overall performance of the disc drive system. Because this rotational accuracy cannot be achieved using ball bearings, disc drives currently utilize a spindle motor having fluid dynamic bearings between a shaft and sleeve to support a hub and the disc for rotation. One alternative bearing design is a hydrodynamic bearing.
In a hydrodynamic bearing, a lubricating fluid such as gas or liquid or air provides a bearing surface between a fixed member and a rotating member of the disc drive. Hydrodynamic bearings eliminate mechanical contact vibration problems experienced by ball bearing systems. Further, hydrodynamic bearings can be scaled to smaller sizes whereas ball bearings have smallness limitations. Efforts have been made to design smaller profile disc drives without loss of performance including maintaining low power consumption. One reduced sized disc drive having a 5 mm thickness currently on the market is the one-inch disc drive used with a CF card type II form factor.
In reducing size, there is a trend to reduce the axial height of the fluid dynamic bearing motor. The axial height of a gap between the base plate and the magnet is one motor section of interest to be minimized. Two types of base plate materials are currently utilized for a 1-inch disc drive, namely, aluminum and steel. While a stamped and machined steel base plate is less expensive and stiffer than casted and machined aluminum, as a steel base plate is positioned increasingly closer to a magnet, bearing friction and power consumption increases, resulting in a start-up delay due to magnetic flux and attraction force between the magnet and the steel base plate. Therefore, simply reducing the gap between the magnet and a steel base plate is unsatisfactory and problematic.
A demand exists for smaller mobile applications including smaller portable computers, and it has become essential in the industry to design disc drives having even smaller dimensions while maintaining motor stiffness and low power consumption. For example, a CF card type I form factor requires a disc drive having a 3.3 mm thickness but such disc drive does not currently exist. Space constraint, stiffness and low power consumption design issues currently remain unresolved. What is needed is a hard disc drive having a 3.3 mm thickness or less, which meets stiffness, power consumption, vibration and acoustic requirements.